The present invention relates to a composition which in the form of a dried film is waterproof and elastic, and has particular advantages as a coating for roofs and walls.
Certain applications for waterproof coatings have the most stringent properties required for the applications to be successful. These stringent property requirements are usually orders of magnitude greater than the property requirements for more conventional coatings, such as conventional house paints. The use of traditional mastic compositions will generally result in an initially waterproof coating. However, the conventional mastic coating has almost no ability to absorb movement of the underlying surface, either by crack development or by shifting of roof tiles or the like, unless applied in relatively heavy thick coatings. In this regard, most mastic coatings will be applied at a total film thickness in the neighborhood of 30 or 40 mils or even more. These coatings are quite difficult to apply to roofs of cement tile or similar structures.
Because of the quite thick coatings which are required for the successful use of conventional mastic coatings, the economics of the coating system are not particularly attractive, even though in some instances relatively cheap starting materials are used. Mastic coatings generally lack the desired degree of adhesion, and have little or no moisture vapor transmission ability. Thus, moisture which may be trapped underneath the coating, or which passes from underneath the roof to the coating-roof interface, is most likely to cause blistering and adhesion failure of the mastic coating. This can rapidly lead to failure of the entire coating.
Furthermore, the high viscosity of the mastic coatings allows little if any penetration into layers of gravel which are commonly found on flat roofs. With the mastic sitting on top of the gravel, little or no adhesion will exist between the coating and the roof underlying the gravel.
The prior art mastic-type roof coatings described hereinabove generally had to be quite thick, due to the relatively low level of physical properties of the mastic composition. Many of these mastic compositions were based upon relatively low cost components, but because of the significant amounts of material required to produce an acceptable waterproof layer, the prior art coatings were not economical. Many leaks in roofs were most difficult to patch with the prior art coating compositions, especially in the case of gravel roofs. In order to insure the best roof patch, it was normally necessary to remove the gravel from the area to be patched, or else to put a coating of mastic over the entire roof.
Acrylic resins of the acrylate and methacrylate type have been used for several decades in conventional house paints, of both the flat and gloss type. Normally the paints will exhibit a pigment volume concentration, or PVC, of at least 8-20, and in the case of flat paints, the PVC may be as high as 50-65 or even higher. Such high levels of pigment generally result in relatively poor extensibility properties of the resulting film. The prior art has been reluctant to utilize acrylic resins at a PVC level below about 20, as the resulting paint generally has poor hiding power, such that it would not be considered a satisfactory paint.
U.S. Pat. No. 3,142,578 is directed to a finish coat for roofs, and is based on an asphalt emulsion, glass fibers, and hogs' hair. The asphalt emulsion has a high solids content, and is used in very high amounts in the final composition, so that the final content of asphalt in the coating may be as high as 60% or so. The patent teaches that the use of hogs' hairs is absolutely necessary in order to obtain an acceptable coating, and that the asphaltic emulsion alone cannot be used as a final sealing coat, as the resultant film checks and pin holes and has other imperfections develop (note column 2, lines 23-26). Various types of asphaltic emulsions can be used, of the nature described at column 5, lines 3-26.
U.S. Pat. No. 3,741,922, discloses aqueous latex paint compositions which are an intimate blend of cellulose esters. U.S. Pat. No. 3,725,328 discloses latex coating compositions adapted for airless spray applications, having pigment volume concentrations in the range between about 45% and about 70%. A number of various types of latexes can be used, including acrylic polymer and copolymer latexes.
U.S. Pat. No. 2,372,108 relates to viscous thixotropic emulsions of acrylate and methacrylate polymers. The polymers are prepared by use of cation-active emulsifying agents, used in a particular manner of polymerizing the corresponding monomeric materials to form the acrylate or methacrylate polymer.
U.S. Pat. No. 3,810,852 discloses thixotropic aqueous dispersions of polymers suitable for use as emulsion paints, wherein the thixotropic agent is a zirconium carbonate complex. U.S. Pat. No. 3,955,997 discloses a semi-solid emulsion coating composition containing a polymeric component, including acrylic resins, a water-soluble organic solvent, a thixotropic material, and a hydrophilic polymer, such as certain cellulose derivatives.
U.S. Pat. No. 3,849,357 discloses pigmented masonry water-repellant compositions, which compositions contain pigment, acrylic polymers, and a silicone resin.
U.S. Pat. No. 3,950,283 discloses the production of multi-colored paint, by admixing two or more differently colored hydroxyethyl cellulose-containing aqueous polymer emulsions, together with a clay dispersion, to form a dispersion wherein the aqueous polymer emulsion particles are the disperse phases in a continuous phase of the clay dispersion.
U.S. Pat. No. 3,505,509 discloses a rubber latex roofing composition. The roofing composition also includes glass fibers, and can contain a surface active agent, an antioxidant, a filling agent, a thickening agent, a wetting agent and a curing agent. Normally the latex constituent is employed in a ratio of 1.2:1 to about 1.5:1 with respect to the glass fiber constituent.
U.S. Pat. No. 3,799,902 discloses a coating composition containing sodium aluminate, and a dispersion of a polymeric latex based on an anionic vinyl-addition polymer, and a water-soluble cationic polymer. The total amount of polymer present in the dispersion is indicated to be within the range of 0.001% to 0.75% by weight. The coating composition is indicated as suitable for forming films which can be cast on surfaces such as glass or metals, or can be used for coating fibers, or corrosion-resistant coatings.